|MA, QING - ETS, INC.,WHEATON, MD
|Wauchope, Robert - Don
|AHUJA, LAJPAT - USDA-ARS FT.COLLINS, CO
|MA, LIWANG - USDA-ARS FT.COLLINS CO
|MALONE, ROB - USDA-ARS AMES, IA
Submitted to: Pest Management Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/29/2003
Publication Date: 3/20/2004
Citation: Ma, Q.L., Wauchope, R.D., Rojas, K.W., Ahuja, L.R., Ma, L., Malone, R.W. 2004. The pesticide module of the root zone water quality model (rzwqm): selected algorithms demonstration and sensitivity testing for pesticide. Pest Management Science 60:240-252(2004).
Interpretive Summary: This report describes some results of testing the ARS RZWQM computer simulation model, a comprehensive computer model designed to predict the fate of pesticides and fertiliser chemicals in the soil. The model attempts to predict the particular combinations of weather, soil, crop and chemical that will lead to water pollution by such chemicals, by simultaneously simulating all the processes, such as degradation by soil microbes or washoff from leaves by rain, that will promote or hinder such chemicals getting into nearby streams or well water. RZWQM is at a stage where it is being used by a few scientists but it is so complex its properties are just being explored in detail. This manuscript reports an examination of a few of the model's capabilities and shows some examples of its predictions. It appears that the model is "behaving" as we would like it to, although one process appears to be programmed wrong. Pollution potential predictions correctly depend on such parameters as soil porosity and rainfall intensity. In particular RZWQM's unique capability to analyze two processes--pH-dependent soil sorption and foliar deposition/decay--that can drastically change a pesticide's pollution potential, is demonstrated. This capability should make RZWQM superior to any other model for predicting the pollution potential of certain newer classes of pesticides.
Technical Abstract: The Root Zone Water Quality Model (RZWQM) is a one-dimensional, numerical model for simulating water movement and chemical transport under a variety of management and weather scenarios at the field scale. The Pesticide Module of RZWQM includes detailed algorithms that describe the complex interactions between pesticides and the environment. We simulated a range of situations with RZWQM including foliar interception of a multiply-applied insecticide (chlorpyrifos) to a growing crop and herbicides (atrazine, flumetsulam) with pH-dependent soil sorption, to examine whether the model appears to generate reasonable results. The model was also tested for the sensitivity of its predictions of chemical fate and water and pesticide runoff to various input parameters. The model appears to be uniquely able to generate reasonable representations of foliar/soil partitioning of foliar-applied chemicals, and the sorption of weak acid and base pesticides, processes which are becoming increasingly important for adequately describing the environmental behavior of newer pesticides. However, the kinetic pesticide sorption algorithm appears to be faulty. Of the 25 parameters and variables analyzed, pesticide half life, Freundlich adsorption exponent and rainfall characteristics were most sensitive for predictions of chlorpyrifos concentration dynamics on corn and in soil. Soil water content at 33 kPa suction head, soil bulk density, saturated hydraulic conductivity of the soil and surface crusts and rainfall were most sensitive for water runoff prediction. Water-phase runoff loss of chlopyrifos was most sensitive to rainfall characteristics.